To allow for people having speech and/or hearing disabilities that prevent them from using conventional telephones to communicate over the public switched telephony network, text telephones or teletypewriters (TTY devices), also known as telecommunication devices for the deaf (TTD devices) have been developed. In general, such devices encode characters of text using sequences of audible tones. In particular, in response to receiving a command to transmit a character, a TTY device will generate a sequence of audible tones that is transmitted through the telephone network to a similar TTY device at the receiving end. The TTY device at the receiving end decodes the sequence of audible tones, and displays or otherwise outputs the encoded character.
In the United States, TTY devices communicate with one another using a 45.45 baud frequency shift key protocol defined in ANSI/TIA/EIA 825 “A 45.45 Baud FSK Modem,” commonly referred to as Baudot signaling. Baudot signaling transmits characters using a sequence of seven audible tones at either 1400 Hz or 1800 Hz. As shown in FIG. 1, a Baudot or TTY character 100 comprises a start tone 104 of 1800 Hz, five tones 108-124 of either 1400 or 1800 Hz to signal the series of five bits specifying the character, and a stop tone 128 of 1400 Hz. The stop tone 128 is a border separating this TTY character 100 from the next. To provide both numbers, letters, and punctuation marks, each TTY endpoint operates in two modes, namely a number/figure mode and a letter mode. Communication between two persons using standard TTYs can only occur in one direction at a time. Thus, the communicants must take turns sending and receiving.
Because the TTY protocol can be slow and tedious for users and requires both endpoints to be configured for TTY generation and transmission, other telecommunication features have been used to provide substantial benefits to persons with hearing and voice impairments. For example, Voice over IP or IP telephony can provide both audio and video speaker feedback to a listener. The ability of a listener to read lip movements synchronized with speech can compensate a listener for up to 20 db of hearing loss. Moreover, sign language can be conveyed to the listener much faster than TTY characters can be inputted and transmitted by the speaker.
Unfortunately, the communication network's desire to allow maximal use of network resources to the broadest number of people can severely impair the abilities of disabled persons to use the network effectively. For example, an audio coder/decoder or codec standard of G.729 (which is commonly employed to conserve bandwidth) will interfere with the effective transmission of TTY tones while the G.711 code standard will not. A slow video refresh rate, low screen resolution, and/or poor degree of synchronization between audio and video streams, which are often employed to conserve bandwidth, can interfere dramatically with a listener's ability to compensate for hearing loss by reading the speaker's lips.
Moreover, when people (illustratively agents in a Public Safety Access Point) receive an emergency call from an unknown party who has a disability (illustratively, a hard-of-hearing person who uses a TTY), the process by which the called parties identify the caller's disability-related communications needs and then adjust themselves appropriately can be cumbersome, and time-consuming It is important to note that, unlike computer modems and fax machines, TTY devices do not emit a “handshake tone,” thereby making it considerably more difficult for network resources to determine automatically, during the call set-up process, that a TTY is in use. For example, when a PSAP answers a call to a universal emergency number the agent responds with a standard spoken greeting and typically receives a silent, open line in return. After waiting an appropriate period of time, the agent queries the line verbally a second time. If the same response is received, the agent (after a substantial amount of time has expired since the call was received) queries the line using a TTY to determine if the call is from a TTY user. This prolonged delay can be fatal to the caller in certain types of emergency calls. Similar prolonged call delays are encountered when a non-disabled person initiates a call to an individual who turns out to have a communication-related disability.
TTYs have been modified to reduce the delay but the modified TTY s either require manual input or are not widely in use. Some TTY devices have the ability to generate a voice announcement, namely “I am a TTY user”. The TTY triggers the announcement in response to manual user input. Such input is not always done by the caller, particularly in an emergency situation. Some TTY s use a proprietary protocol developed by UtraTec™ that can detect automatically a TTY user at the other end of the call when a specific acoustic signal from the other end is detected. However, if the acoustic signal is absent because the sending endpoint is not configured to send the signal or the signal is lost or corrupted during transmission, the receiving endpoint will not detect automatically the sending TTY and fail to reconfigure itself accordingly.
Currently, networks have only a limited ability to reconfigure themselves based on user needs and particularly disabled user needs. It is important to note that many TTY devices are used in conjunction with standard telephone endpoints, and are connected to these telephones by placing the phone's handset into an acoustic coupler on the TTY. For this reason, it is not possible to rely on a telephone of the prior art to provide appropriate TTY-specific call set-up information. For example, Information Indicators or II digits in the Integrated Services Digital Network protocol allow for a network to reconfigure itself based on the characteristics and/or permissions of the calling terminal. In the Session Initiation Protocol or SIP, a presence server maintains information regarding not only the user's presence and availability but also the capabilities (e.g., supported codecs) of his or her associated communication devices. This information, particularly information about the capability of an endpoint, is provided as part of the call set-up handshake procedures. In many contact centers, caller identifiers have been used to determine routing destinations and cause information associated with the identified caller to be retrieved and provided to the agent assigned to service the caller. It has been suggested by Henning Schulzrine, in a document entitled “Emergency Call Services for SIP-based Internet Telephony”, that the call setup can provide additional medical background, without having to store the information in a central database and that the ability to indicate language capabilities of the caller can help route the call to an operator, without the additional delay of having a general operator try to ascertain the language of the caller.
Nothwithstanding these limited measures, there remains a need for a communications network that can configure or reconfigure itself automatically to reflect the unique demands imposed by a telecommunications interaction with a disabled person.